481 



tum pellucidum. These two limbs of the commissure meet posteriorly 

 in a »splenium commissurae fornicis« and include between them the 

 thickening of the lamina terminali» , which in higher mammals be- 

 comes stretched and otherwise modified by the growing commissure 

 to form the septum pellucidum. 



d. The fibres homologous to the corpus callosum (commiss ura 

 pallii dorsalis) of Eutheria, form part of the anterior commissure 

 (commissura hemisphaerium ventralis) in the Meta-, as also in 

 the Proto-, theria. 



e. As there is no proper corpus callosum the anterior extremity 

 of the hippocampus does not atrophy, as it does in the Placentalia to 

 form gyrus supracallosus and striae Lancisii. 



f. Associated with the fact that the hippocampus is not disturbed 

 by a dorsal palliai commissure, the fornix is not divided into a f. lon- 

 gus and obliquus, nor is there any division into psalterium dorsale and 

 ventrale in the sense of Honegger. 



g. There is a well marked olfactory ventricle communicating with 

 the anterior horn of the lateral ventricle. 



Individual features of the cerebrum of Notoryctes. — 

 It is characterised by the possession of a huge olfactory bulb , which 

 is half as long as the hemisphere proper, and , as in the reptile-brain, 

 is placed entirely in front of (i. e. not overlapped by) the cerebrum. 



Associated with the large size of the olfactory bulb , there is a 

 huge tuberculum olfactorium (quadrilateral space of Broca) forming a 

 large hemisphere extending as far as the lateral aspect of the hemi- 

 sphere. 



The large pyriform lobe not only forms the whole of the rest of 

 the basal aspect of the cerebrum but also the greater part of its lateral 

 aspect. The nucleus amygdalae is correspondingly large. In spite of 

 the fact that it forms part of the smell-centre the hippocampus does 

 not appear to be enlarged proportionately to the olfactory bulb. 



The pallium (Turner) is relatively much smaller than in any 

 other mammalian brain with which I am acquainted. 



Associated with the small size of the pallium the characteristic 

 inroUing and folding of the hippocampus is much slighter and simpler 

 than in any other mammalian (including the raonotreme) brain. 



In spite of the fact that the pallium is markedly smaller , both 

 actually and relatively, than the corresponding structure in both Mo- 

 notremes, the bending of the hemisphere is developed to a much grea- 

 ter extent in the Marsupial. As a consequence of this bending the 



